1. Field of the Invention
The present invention relates to a perimeter intrusion detection system with integrated sensor cable. More particularly, the present invention relates to a security sensor system, with a specific cable configuration, for locating a disturbance along the length of the sensor cable and for providing intrusion data through a further use of the sensor cable.
2. Description of the Prior Art
In the field of outdoor intrusion detection systems, there are many security systems for sensing disturbances along a distributed sensor cable deployed about a perimeter. These systems face certain challenges not found in indoor security situations. Environmental conditions, such as temperature extremes, rain, snow, animals, blowing debris, seismic effects, terrain and traffic, must all be taken into account. When functioning under these adverse conditions, the system must continue to maintain a high probability of detection while minimizing false alarms (alarms with unknown causes) and nuisance alarms (environment-related alarms), both of which may compromise and reduce the performance of the security system.
Fence and wall-associated sensors are above-ground detection sensors that are attached to an existing fence or wall. They detect intrusion when an intruder disturbs the detection field, or when strain or vibration due to cutting or climbing on a metal fabric fence triggers an alarm. IntelliFIBER™ is a fiber-optic based fence-disturbance sensor for outdoor perimeter security applications from Senstar-Stellar Corp., of Carp, Ontario, Canada. This prior art fiber optic sensor can detect intruders cutting, climbing, or lifting fence fabric, and it provides protection circuitry against electromagnetic interference, radio frequency interference, and lightning. The system includes a programmable microprocessor that processes signals based on the changes in optical parameters generated as a result of disturbances in proximity to the distributed fiber optic sensor cable. The microprocessor allows the user to calibrate and set operating parameters for specific zones/environments. Alarm processing optimizes detection and minimizes nuisance alarms from wind, rain, snow, fog, animals, debris, seismic activity, and the like.
In many security systems, one important characteristic which is useful to determine in conjunction with suitable processing means, is the location of the disturbance along the length of a sensor cable. Such a characteristic is commonly known in the art as “ranging”. Ranging is useful both to identify the intruder, but also to locate and rectify locations where nuisance alarms are generated, for example a loose sign banging on the fence.
In any intrusion detection system, the ability to minimize false or nuisance alarms is enhanced when better information on the intrusion event is obtained. Hence, location data, and/or simultaneous data from two or more detection phenomenologies, is useful data to fuse for processing to further obtain either a higher probability of detection, a lower false alarm rate (FAR), a lower nuisance alarm rate (NAR), or a combination.
In the prior art, there are various security systems having a ranging capability. For instance, U.S. Pat. No. 5,446,446, issued to Harman, discloses a transducer cable for detecting the location of a sensed disturbance along the length of the transducer cable. A “driving” signal is imposed on the transducer cable in order to obtain a response signal. According to Harman, the location of the intruder is determined from the detected response signal. While ranging capabilities of a transducer cable are taught by Harman, the specific transducer cable design is costly, and only allows detection by a single means, namely an impedance change. In another related U.S. Pat. No. 5,448,222, a single means is also disclosed.
Another Harman published patent application, US 2002/00441232, discloses a cable guided radar system for the detection and location of an intruder. The cable system comprises a pair of leaky coaxial cables coupled to an RF transceiver which is in turn coupled to a processor. However, the dual leaky coaxial cable structure is very expensive to produce, requires the generation and reception of an external electromagnetic field, and provides only a single detection signal caused by the motion of a target in the field. Additionally, sensing a target within an external field has not been found to be a practical application for mounting on metal structures, such as fences, nor typically above ground such as on walls.
The U.S. Pat. No. 5,705,984, issued to Wilson, discloses a sensing system with a deformable sensor cable utilizing a reflectometer to measure the reflected signal. The deformable sensor cable of the Wilson patent discloses a ranging capability where an RF signal is injected along the sensor cable and the reflected signal measured. However, a deformable cable requires that the cable be compressed to detect an intrusion rather than sensing movement of the conductor. In the U.S. Pat. No. 3,846,780, issued to Gilcher, while a loose centre conductor in tube is disclosed, a sensor cable system with a ranging capability is not provided. Neither reference discloses a dual use sensor cable for ranging and for processing of detection data, as well as a suitable cable configuration for such dual purposes.
In view of the above-noted shortcomings, the present invention seeks to provide an intrusion detection system (IDS) with an integrated sensor cable having a multi-purpose application to provide additional intrusion data in a security sensor system. In addition, the present invention seeks to provide a sensor cable utilized for ranging purposes in combination with at least one parallel passive or active sensor cable utilized for intrusion detection purposes, to form an integrated sensor cable.